1. Field of the Invention
The present invention relates to an improvement in a process of applying a liquid coating composition to a continuously moving long flexible support, hereinafter referred to as "web". This process is used in manufacturing photosensitive or photoengraving materials, such as photographic film, photographic printing paper, and the like, magnetic recording materials, such as magnetic recording tape and the like, or recording materials, such as pressure-sensitive recording paper, thermosensitive recording paper and the like. More particularly, the invention relates to a coating method and apparatus for applying a freely falling coating composition to a web which is continuously moving on a backing roll.
2. Background of the Invention
In a conventional coating process, a thicker region of the coating film is formed at widthwise edges of a web due to the interfacial tension of the coating composition. The thicker coating film portion at the edges of the web causes irregularity of dryness in a drying process after coating. Therefore, it has been desired to remove the thicker coating film portion before a drying process. A method and apparatus improved in such a process has been disclosed in U.S. Pat. No. 2,899,339. Apparatus of this patent comprises a vacuum nozzle having a chamber within, means for connecting the nozzle with a source of vacuum, an opening in the nozzle, means for introducing into the chamber adjacent said opening a diluent for the coating, and means for guiding the nozzle against a lateral edge of the moving web with the opening positioned over the lateral edge.
Further, a method for producing a coating has been proposed in Japanese Unexamined Patent Publication No. 73579/1981. According to this reference, a liquid is jetted to a thicker coating film portion from the center portion of a function nozzle having the same double pipe structure as described. Then the liquid is sucked into the suction nozzle together with a coating composition at the thicker coating film portion.
Further, a method has been proposed in Japanese Unexamined Patent Publication No. 75354/1985 by the same inventors as those of this application. According to this reference, thicker coating portions at the edges of a coating layer are removed by an endless belt.
However, after the investigation of the coating process disclosed in the U.S. Pat. No. 2,899,339, the inventors of this application have found that it is difficult to keep a balance between the jetted solution or jet stream of the diluted solute and solvent supplied to the end portion of the suction nozzle and the suction force of the center portion of the nozzle. Accordingly, the treatment for the edges of the web is insufficient. Further, the method disclosed in the Japanese Patent Unexamined Publication No. 73579/1981 has a disadvantage in that the liquid jetted from the center portion of the suction nozzle having the double pipe structure becomes attached to the rear surface of the web, that is, the surface opposite to the surface of the web to which the coating composition is applied. Another disadvantage is that pass rollers in the vicinity of the web are stained by the liquid.
Furthermore, the method disclosed in the Japanese Patent Unexamined Publication No. 75354/1985 has an advantage in that a good coating can be made without producing a thicker coating at the edge of the web, but it has an disadvantage in that equipment relevant to the endless belt is large-scaled.